This invention relates to an epoxy resin composition having superior moisture proofness and long-term stability, an epoxy resin composition for encapsulation, an epoxy resin composition for a laminated plate, and an epoxy resin composition for a solder resist.
Recently, in keeping up with rapid progress in the scientific technology centered around the electronic industry, a demand on a variety of electrical equipments and the material therefor is becoming more and more stringent. Above all, the progress in the semiconductor-related technology is outstanding, such that the integration degree of semiconductor memories is becoming higher and, in keeping pace therewith, there is a marked tendency towards finer interconnection and larger chip size. On the other hand, with the improved integration degree of semiconductor memories, surface mounting is adopted as a mounting method in preference to through-hole mounting. However, in line automation of surface mounting, a problem is raised in that upon soldering lead wires, a semiconductor package undergoes acute changes in temperature, as a result of which the resin molded part is cracked or the interface between the lead wire and the resin is deteriorated to lower moisture proofness.
For overcoming the above inconvenience, a variety of resin compositions for semiconductor encapsulation for relieving thermal impact on immersion of a semiconductor package in a soldering bath have been proposed. For example, resin compositions admixed with silicon compounds or thermoplastic oligomers or silicon-modified resin compositions have been proposed. However, with these compositions, molded products are cracked after immersion in a soldering bath, such that reliable resin compositions for semiconductor encapsulation have not been realized.
As for phenol resins employed as curing agents for the epoxy resins as main components of the resin composition for semiconductor encapsulation, dicyclopentadiene-modified phenol resins have been proposed as heat-resistant phenol resins having excellent moisture proofness in preference to customary novolak phenol resin or novolak cresol resin (Japanese Laid-open Patent Application No.63-110213). However, these dicyclopentadiene-modified phenol resins are low in reactivity and have higher softening points, while being inferior in moldability, so that it is not possible to prevent cracking on immersion in the soldering bath completely.
Novolak epoxy resins are mainly employed as the epoxy resin used for a resin composition for semiconductor encapsulation. Recently, for overcoming the above-mentioned problems, an epoxy resin produced by diglycidylating a bivalent phenol compound such as bisphenol compound or bishydroxy naphthalene, has been proposed and employed. Although the epoxy resin has a high glass transition temperature Tg of the cured product and the amount of addition of inorganic fillers can be increased, despite its low molecular weight, the produced cured product is not satisfactory in flexibility, while being inferior in moisture proofness.
In the field of high-speed electronic equipment, in keeping pace with the tendency towards high density of electronic elements, high signal rate and high frequency, problems have been raised in connection with delay in signal transmission in the materials of high-speed electronic equipments or heat evolution in various devices. Since the delay time in signal transmission is increased in proportion to the root of dielectric constant of the printed interconnection plate material, a demand has been raised for materials having a low dielectric constant. However, an epoxy resin laminated plate based on glass cloth extensively used in general as printed interconnection plate material has a dielectric constant as high as 4.5 to 5.0 such that if such laminated plate is used as a material for high-speed electronic equipment or high-frequency equipment, signal transmission with a high enough rate cannot be achieved Although a laminated plate of polyethylene, polytetrafluoroethylene, polyphenylene oxide or polysulfone, has been developed for lowering the dielectric constant, a problem is presented in that since the resin used in the laminated plate is a thermoplastic resin, it is inferior in strength or thermal resistance on soldering. On the other hand, epoxy resins consisting mainly of novolak epoxy resin and admixed with bromated epoxy resins with a view to retardation of combustion have been employed as the epoxy resins used in general in epoxy resin laminated plates. However, since the resin owes its dielectric properties in a majority of cases to the structure of the epoxy resins employed, a demand has been raised for an epoxy resin which may be used as a material for printed interconnection circuit for a high frequency equipment and a high-speed electronic equipment in place of the novolak epoxy resin, and which is superior in dielectric properties. However, such resin has not been developed to data.
On the other hand, a solder resist is a material which is applied at the time of soldering an electronic component to a printed interconnection circuit to sites other than those intended for soldering for the purpose of preventing the solder from becoming affixed or for protecting the interconnection circuit. Consequently, thermal resistance on soldering, resistance to water-soluble fluxes, electrical insulating properties, tight bonding and excellent properties on pressure cooker tests (PCT) are demanded of the solder resist. Besides, the solder resist is directly used in a majority of cases as a plating resist, in which case resistance to alkali, resistance to acid and resistance to plating are demanded of the solder resist.
Various types of the solder resist are used depending on the usage and application. For example, epoxy-based thermosetting resist inks are employed for industrial printed boards, whilst UV curable type resist inks are mainly employed for consumer printed boards. Recently, dry film type solder resists in the form of photosensitive films or liquid photosensitive solder resists capable of forming fine-line interconnections, are frequently employed. However, since thermal resistance on soldering, resistance to water-soluble fluxes, electrical insulating properties, tight bonding and excellent properties on PCT are demanded of the solder resist, epoxy resins such as novolak epoxy resins are contained as essential components in the solder resist. However, the thermal resistance on soldering, tight bonding, resistance to chemicals, etc. recently demanded of the solder resist, are not met with the customary epoxy resin. Besides, the photosensitive solder resist suffers from the problem that if the ratio of the epoxy resin is increased for improving the above-mentioned properties, the resulting composition is lowered in photocurability so that an unexposed portion is lowered in developing properties to render it impossible to form satisfactory resist patterns or to lead to inferior plating resistance. Besides, if the novolak epoxy resin is mixed into the solder resist, a cured film is inferior in flexibility. For these reasons, a demand is raised for an epoxy resin free of the above-mentioned drawbacks.